Falls are by far the leading cause of accidental injury and death in older adults. The Veteran population is more severely affected by falls since it is significantly older than the overall population (45% over 65 years of age vs. 13%), and has a higher prevalence of disability. Thus, Veterans would benefit substantially more from an accurate diagnosis and treatment of balance function. Despite its importance, much is still unknown about the manner in which balance is compromised by age and disease. Therapeutic interventions for people who are at risk of falling have proven to be of limited utility. Engineering methods are well suited to study and evaluate balance; but have to date been applied to overly simplified scenarios that lack the complexity to probe the musculoskeletal and neurophysiological bases for balance and falls. The long term objective of this research, which began with a VA Rehabilitation Research & Development (RR&D) Career Development Award (CDA-2), is to develop improved directives and protocols for the diagnosis and treatment of balance-related posture and movement coordination problems. This proposal significantly advances engineering and psychophysical methods to address existing gaps in the diagnosis and treatment of balance impairments through the development of a Balance Assessment and Training Platform (BATP). The goal of the BATP is to quantitatively assess and improve at-risk individuals? ability to maintain balance when disturbed by volitional movements of the body and its parts?an important class of balance disturbances integral to many activities of daily living that can precipitate falls. The BATP?s Assessment Module quickly establishes the subject?s Limit of Balance (LoB), and then measures performance in a reaching task while at the LoB. These better expose balance deficits for identification and evaluation. The BATP?s Training Module?s goal is to increase subjects? LoB by continuously challenging them to perform the reaching task at their current LoB, and when they demonstrate proficiency expanding the reaching task to increase their LoB. The BATP focuses on performance at and just beyond the limits of balance, unlike most such tests and training protocols that do not challenge subjects in this way. The BATP?s most immediate and salient metric is the LoB for standing reach; and we hypothesize that expanding this LoB, as the BATP is designed to do, will improve balance function and make individuals more resistant to falls (in the context of expected balance disturbances). Confirmation of this hypothesis could provide a new perspective on existing training protocols? modest success rates, and direction for the design of new protocols with the potential to significantly improve these rates. We believe that the performance metrics and analytical results produced by the BATP can form the basis for new diagnostic measures that more reliably and precisely quantify and explain balance performance problems; as well as have the sensitivity to track changes in them over time. Such diagnostic and treatment protocols would be particularly beneficial to the VA Health Care System, as it would lead to improvements in: patient throughput, quality of care, and treatment costs. Though this proposal targets the aging Veteran stroke population, the BATP is a general tool that can aid in the diagnosis and treatment of balance disorders arising from conditions other than stroke. These include obesity, diabetes (which often leads to lower extremity muscle degeneration and peripheral neuropathy), sarcopenia, vestibular disorders, and otherneurological disorders such as Parkinson?sdisease. Veterans whose balance has been compromised by TraumaticBrainInjury(TBI?whether combat-related or not) may also benefit from these tools.